(1) Field of the Invention
The present invention relates to a circulating type grain drying machine for drying grains, for example, an unhulled rice, wheat, etc.
(2) Description of the Related Art
Conventionally, there is a circulating type grain drying machine in which, for reducing the time required for drying, separately from a drying section for drying grains with heated air being supplied, there is provided a heating section for preliminarily increasing the temperature of grains (hereinafter referred to as a "grain temperature").
For example, Japanese Patent Application Kokai Publication No. Sho 62-9174 discloses a circulating type grain drying machine for providing preliminary heating to grains, which is provided, sequentially from the top thereof, with a reservoir section for temporarily keeping grains, a heating section having a plurality of heating pipes through which the heated air generated by one burner passes, and a drying section for drying the grains by heated air introduced from each of the heating pipes.
Also, Japanese Patent Application Kokai Publication No. Hei 2-309177 discloses a machine which is provided, sequentially from the top thereof, with a reservoir section, an upper drying section for effecting preliminary heating of grains equipped with a first burner, and a lower drying section for drying the grains also equipped with a second burner.
Further, Japanese Patent Application No. Hei 10-265486 in which the applicant is the same as in the present application discloses a machine which is provided, sequentially from the top thereof, with a reservoir section, a heating section for effecting preliminary heating of grains equipped with a plurality of heating pipes through which the heated air produced by a heating means passes, and a drying section for drying the grains by the heated air produced by a heating means provided separately from the above heating means.
In the above respective conventional circulating type grain drying machines, there are respectively the following problems:
With respect to the conventional machine disclosed in Japanese Patent Application Kokai Publication No. Sho 62-9174, the heated air generated by one burner passes through and heats each heating pipe and the heated air, after the heat is taken by the heating pipes with the heated air resulting in a lower temperature, is introduced into the drying section and serves as the heated air again for drying the grains. In order to introduce heated air of a predetermined temperature into the drying section, it is necessary to raise, according to the predetermined temperature, the temperature of the heated air for heating the heating pipes. Hence, in the disclosed machine, the heating pipes cannot be heated sufficiently. Also, since the heating temperature of the heating pipes and the heated air temperature of the drying section cannot be controlled separately, a drying efficiency may not be satisfactory.
In the conventional machine disclosed in Japanese Patent Application Kokai Publication No. Hei 2-309177, the drying is carried out by supplying to the grains in the upper drying section the heated air of high temperature and of small amount of airflow and, after the grain temperature has been raised, the grains are then subjected to the heated air of low temperature and of large amount of airflow in the lower drying section. Since the grains are exposed to the heated air for a long time at both the upper and lower drying sections, the quality of the grains will be affected and aggravated. Also, since the upper drying section and the lower drying section are provided respectively with separate burners, the quality deterioration of grains as mentioned above is caused thereby and, since the heated air at the upper drying section is not utilized in the lower drying section, the drying efficiency will not be satisfactory and the improvement is desired.
In the machine disclosed in Japanese Patent Application No. Hei 10-265486, the heating section and the drying section are respectively provided with heating means. After the grains are subjected to a preliminary heating through the heating pipes heated up to a predetermined temperature by the heating means of the heating section, the heated air which is produced separately from the above heating means and which is lower than the grain temperature is supplied to the grains in the drying section whereby the grains are efficiently dried while the quality deterioration is being prevented. However, in this drying machine, the heating temperature of the heating pipes is set to a predetermined constant temperature, and the heated air supplied to the drying section is made lower than only the grain temperature produced by the heating section. Thus, the arrangement was not one in which, in consideration of the grain water content which varies as the drying operation progresses, the heating temperature of the heating pipes and the heated air temperature supplied to the drying section are respectively controlled to optimum temperatures. Also, the heating section and the drying section are provided with separate heating means, and the heated air of the heating section is simply exhausted to outside the drying machine. Thus, the improvement is desired in the aspect of the drying efficiency.